Thermal dye transfer image-receiving sheet

Abstract: A sheet of the type which comprises a release base sheet and a thermal transfer image-receiving layer formed on the release base sheet and which is capable of releasing the thermal transfer image-receiving layer from the base sheet is described. The receiving layer is made of a dispersion, in a resin binder, of a layer compound capable of fixing cationic dyes through ion exchange reaction therewith. The receiving layer can be readily formed on a desired type of substrate by superposing the receiving layer on the substrate, after which the release base sheet is peeled off from the receiving layer. A thermal transfer image can be formed on the receiving layer by superposition with an ink ribbon containing a cationic dye and application of image information to the ink ribbon or by re-transfer of a cationic dye image from a printing paper. The thermal transfer image may be formed prior to the transfer of the receiving layer on the substrate. Owing to the fixing of the cationic dye through ion exchange reaction, the fixing properties of the dye in the receiving layer can be significantly improved.

Description: The invention relates to a method for forming a thermal transfer image on a substrate, the method comprising the step of providing a printing sheet comprising an image-receiving layer on which a thermal transfer image made of a cationic dye has been formed. Sublimation transfer recording techniques have wide utility in the fields where video image information is fixed, as a thermal transfer image, on an image-receiving layer of a material to be transferred. The material to be transferred which is ordinarily employed is a printing sheet including a substrate and an image-receiving layer capable of receiving dye images thereon. Using this type of printing sheet, the thermal transfer image is formed by procedures wherein the ink layer of an ink ribbon having thermally diffusable dyes such as disperse dyes therein is superposed on the image-receiving layer of the material to be transferred and heated by heating means, such as a thermal head, in accordance with image information, thereby causing the dye in the ink layer to be transferred to the image-receiving layer. Recently, the images thermally transferred by the sublimation thermal transfer techniques have been formed on various types of materials or substrates. For instance, typical of such a material is a polyvinyl chloride card (hereinafter referred to simply as PVC card) which has an image-receiving layer consisting of polyvinyl chloride. The thermal transfer image is formed directly on the image-receiving layer of the PVC card. Further, attempts have been made wherein a thermal transfer image has been once formed on an ordinary printing sheet which has , on a substrate, an image-receiving layer made of thermoplastic resins and the thus formed image is re-transferred on a plain cloth such as of cotton. In the case, an adhesive sheet made of a thermoplastic resin is sandwiched between the cloth and the image-receiving layer of the printing sheet, followed by hot pressing by use of a warm iron and peeling off the substrate of the printing sheet to re-transfer the image-receiving layer on the cloth. Alternatively, the dye image alone on the image-receiving layer may be re-transferred to an adhesive sheet sandwiched between the cloth and the printing sheet, followed by peeling off the printing sheet to permit the thermal transfer image to be re-transferred on the cloth. However, when the image-receiving layer on the PVC card on which the thermal transfer image has been formed is brought into contact with materials having large amounts of plasticizers therein, e.g. artificial leathers, soft vinyl chloride sheets, plastic erasers and the like, over a long time, the dye of the thermal transfer image formed on the image-receiving layer is at least partially re-transferred to the material, thereby presenting the problem that the thermal transfer image is damaged. Additionally, ordinarily employed disperse dyes are soluble in organic solvents such as toluene, ethanol and the like. When the image-receiving layer is contacted with such solvents as mentioned above, the dye is dissolved out from the image-receiving layer. This eventually brings about the thermal transfer image being impeded. On the other hand, with the case of the cloth on which a thermal transfer image has been re-transferred, when the cloth is subjected to dry cleaning, the dye is dissolved out in solvents for the dry cleaning, thus impeding the image on the cloth. With the cloth where a dye image alone is retransferred to its adhesive layer, dyes have to be used in larger amounts since known disperse dyes are not satisfactory with respect to the transfer efficiency thereof. EP-A-0 506 034 discloses a method for forming a thermal transfer image on a substrate as mentioned above. The printing sheet used in this method comprises an image-receiving layer on which a thermal transfer image made of a cationic dye has been formed. The thermal transfer image has very good fixing properties which are comparable to silver salt photographic images. US-A-4,923,848 discloses a method for forming sublimation transfer images on a substrate comprising a first transferring step for sublimation transferring images on an image-transferable or printing sheet comprising a sheet-like support and an image-receiving layer provided on one surface of said sheet-like support, said sublimation transferring being carried out by means of a thermal printer on the basis of an image data formulated by an image data processor and a second transferring step for transferring the images formed on the printing sheet from the image-transferable sheet to the substrate. The image-receiving layer is attached to the substrate. SUMMARY OF THE INVENTION It is an object of the present invention to improve the methods known from the state of the art especially with respect to fixing properties and variability of the substrate type such as PVC cards, cloths and the like after or prior to formation of the thermal transfer images. According to the present invention this object is achieved by a method of the above kind further comprising the steps of further providing a sheet of the type including a release base sheet and a thermal transfer image-receiving layer, said thermal transfer image-receiving layer beings made of a dispersion, a resin binder, of a layer compound capable of fixing cationic dyes through ion exchange reaction therewith, superposing the image-receiving layer of the printing sheet on said thermal transfer image-receiving layer of said sheet, hot pressing the superposed layers to re-transfer the cationic dye image on said thermal transfer image-receiving layer thereby causing the cationic dye image to fix through ion exchange reaction with the layer compound in said thermal transfer image-receiving layer. According to a preferred embodiment, the above method comprises the additional steps of superposing said thermal transfer image receiving layer on which a thermal transfer Image is to be formed in a face-to-face relation with the substrate and peeling off said release base sheet from said thermal transfer image receiving layer prior to the step of superposing the image receiving layer of the printing sheet on said thermal transfer Image receiving layer. According to another preferred embodiment, the above method comprises the additional step of transferring the thermal transfer image receiving layer on which the thermal transfer image has been formed to the substrate after the step of hot pressing the superposed layers. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic sectional view of a sheet capable of releasing a thermal transfer image-receiving layer therefrom; Fig. 2 is a schematic sectional view of a sheet capable of releasing a thermal transfer image-receiving layer therefrom; Figs. 3A, 3B and 3C are, respectively, an illustrative view for a method of transferring a thermal transfer image-receiving layer to other substrates; Figs. 4A, 4B and 4C are, respectively, an illustrative view for another method of transferring a thermal transfer image-receiving layer to other substrates; Figs. 5A, 5B and 5C are, respectively, an illustrative view for a further method of transferring a thermal transfer image-receiving layer to other substrates; Figs. 6A, 6B, 6C and 6D are, respectively, an illustrative view for a method of forming a thermal transfer image; Figs. 7A, 7B, 7C and 7D are, respectively, an illustrative view for another method of forming a thermal transfer image; Fig. 8 is an illustrative view showing the structure of a non-treated layer compound; Fig. 9 is an illustrative view of the structure of a layer compound substituted with quaternary ammonium ions; and Fig. 10 is an illustrative view of the structure of a layer compound ion-exchanged with cationic dye molecules. DETAILED DESCRIPTION OF THE INVENTION The invention is described in detail with reference to the accompanying drawings wherein like reference numerals indicate like members or parts. Fig. 1 is a sectional view of a sheet from which a thermal transfer image-receiving layer can be released and transferred to intended types of substrates. As shown in the figure, the sheet has a release base sheet 1 and a thermal transfer image-receiving layer 2 formed on the base sheet 1. The base sheet 1 functions as a support for the image-receiving layer 2. When the layer 2 is released and transferred to other substrates such as PVC cards, the base sheet 1 is peeled off at the interface with the image-receiving layer. The base sheet 1 which is preferably used is an ordinary polyethylene terephthalate film. Of course, there may be used as the release base sheet white opaque sheets such as pearl bases to which white pigments or pealescent pigments are added. In this case, the sheet having the thermal transfer image-receiving layer thereon may be used as a printing sheet as it is. The image-receiving layer 2 is one on which a thermal transfer image is formed. The layer 2 is made of a dispersion of a layer compound dispersed in a resin binder. The layer compound should be capable of fixing cationic dyes through ion exchange reaction therewith. The layer compounds used in the present invention are those compounds which have ion-exchangeable cations inbetween the layers thereof. Such compounds include those compounds which are set out, for example, in United States Patent Application Serial No. 858,650. For instance, clay layer compounds having ion exchangeability and, particularly, montmorillonoids of the following formula (1) may be mentioned as preferred (X,Y) 2∼3 Z 4 O 10 (OH) 2·m H 2 O·(W 1/3 ) wherein X represents Al, Fe(III), Mn(III) or Co(III), Y represents Mg, Fe(II), Mn(II), Ni, Zn or Li, Z represents Si or Al, W represents K, Na or Ca, H 2 O represents intercalated water, and m is an integer. Specific examples of the montmorillonoids of the formula (1) include, depending on the combination of X and Y and the number of substitutions, natural and synthetic products such as of montmorillonite, magnesian montmorillonite, iron montmorillonite, iron magnesian montmorillonite, beidellite, aluminian beidellite, nontronite, aluminian nontronite, saponite, aluminian saponite, hectorite, sauconite and the like. Moreover, there may be used those compounds of the formula (1) wherein the OH group or groups are substituted with a halogen atom such as a fluorine atom. Aside from the montmorillonoids of the formula (1), there may be mentioned other types of cationic exchangeable clay compounds including a mica group such as of sodium silicic mica, sodium taeniolite, lithium taeniolite and the like. The layer compounds should preferably have a satisfactory distance between the layers of the compound so that cationic dyes become more likely to enter the layer structure of the compound whereby the ion exchange reaction readily proceeds. It is also preferred that individual interstices between the layers of the compound are rendered hydrophobic in nature so that the layer compound can be readily dispersed in oleophilic or hydrophobic resin binders. To this end, the cation exchangeable alkali metal cations or alkaline earth metal cations in the layer compound should preferably have been replaced organic cations which are ion exchangeable with cationic dyes and have oleophilic groups. Preferable examples of such organic cations include quaternary ammonium ions or substituted phosphonium ions having an alkyl group which has not less than 8 carbon atoms. In view of the fixing of thermal transfer images and the ease in formation of a thermal transfer image-receiving layer, the amount of the layer compound should preferably be in the range of 10 to 90 wt% of the image-receiving layer as a solid content. The resin binders may be those resins properly selected from thermoplastic resins and thermosetting resins, which are used in the image-receiving layer of printing sheets ordinarily employed for thermal transfer recording. Preferably, there are used thermoplastic resins, such as polyethylene, polyvinyl chloride and the like, which turn into an adhesive on heating thereof. By this, when heating the thermal transfer image-receiving layer 2, adhesion is imparted thereto, enabling one to transfer the layer 2 to other substrates without use of any adhesive. As shown in Fig. 2, there may be formed an adhesive layer 3 on the image-receiving layer 2. This arrangement permits easy transfer of the image-receiving layer 2 to other substrates. The adhesive layer 3 may be made of thermoplastic resins, such as polyethylene, polyvinyl chloride and the like, capable of exhibiting adhesiveness on heating or thermosetting adhesives such as epoxy or urethane adhesives. The cationic dyes which are fixed through ion exchange reaction with the layer compound in the thermal transfer image-receiving layer 2 may include various types of cationic dyes capable of being fixed or held with the layer compound through the ion exchange. Examples include water-soluble dyes such as azo, triphenylmethane, azine, oxazine and thiazine dyes which have, respectively, an amine salt or a quaternary ammonium group. It is preferred that these dyes are subjected to hydrophobic treatment in order to realize rapid ion exchange reaction with a layer compound which is present in a hydrophobic environment. For the hydrophobic treatment, the counter anions of the cationic dyes such as halogen ions are preferably subjected to ion exchange with organic anionic surface active agents having a hydrophobic group, e.g. sulfonates such as alkylbenzenesulfonates, sulfates such as alkylsulfates, carboxylates such as alkyl ether carboxylates, phosphates such as alkylphosphates and the like. The sheet capable of releasing a thermal transfer image-receiving layer therefrom can be fabricated by a usual manner. For instance, a composition for the receiving layer is applied onto a release base sheet by a usual manner and dried to obtain the layer-releasing sheet. If necessary, an adhesive composition may be further applied and dried to obtain the sheet of the type shown in Fig. 2. Then, a method for transferring the thermal transfer image-receiving layer to other substrates such as PVC cards or cloths using the sheet of the invention is described. The image-receiving layer transferring method comprises, as stated hereinbefore, superposing a sheet having an image-receiving layer on a release base sheet on a substrate such as a PVC card or a piece of cloth on which a thermal transfer image is to be formed, in such a way that the image-receiving layer is facing with the substrate, and peeling off the release base sheet from the receiving layer to permit the image-receiving layer to be attached to the substrate. This method is more particularly described with reference to Figs. 3A to 3C, 4A to 4C and 5A to 5C. Figs. 3A to 3C show a procedure of transferring and attaching the image-receiving layer 2 from the layer-bearing sheet to a substrate 4 and fixing the layer 2 on the substrate 4 through a separately provided adhesive sheet 5. The image-receiving layer 2 is provided in face-to-face relation with the substrate 4, between which the adhesive sheet 5 is provided as shown in Fig.3A. The superposed arrangement is then entirely subjected to hot pressing to bond the layer 2 to the substrate 4 through the adhesive sheet 5 as shown in Fig.3B. Finally, the release base sheet 1 is peeled off to transfer the image-receiving layer 2 to the substrate 4. In the case, the adhesive sheet 5 may be a sheet of a thermoplastic resin such as polyethylene, polyvinyl chloride or the like or a thermosetting resin provided that it exhibits adhesiveness on heating. Figs. 4A to 4C show a procedure of attaching the layer 2 to other substrate 4 wherein the layer 2 has adhesiveness when heated. The image-receiving layer 2 and the substrate 4 are provided in face-to-face relation with each other as shown in Fig. 4A, followed by hot pressing to bond the layer 2 directly to the substrate 4 as shown in Fig. 4B. Finally, the release base sheet 1 is separated to attach the layer 2 to the substrate 4. Figs. 5A to 5C a procedure of attaching the layer 2 to the substrate 4 wherein the transfer sheet is of the type shown in Fig. 2 which has an adhesive layer 3 on the layer 2. The adhesive layer 3 and the substrate 4 are provided in face-to-face relation with each other as shown in Fig. 5A, followed by hot pressing to bond the layer 2 to the substrate 4 through the adhesive layer 3 as shown in Fig. 5B. Finally, the release base sheet 1 is separated to attach the layer 2 to the substrate 4. Reference is now made to 6A to 6D and 7A to 7D with which there are illustrated procedures of forming thermal transfer images on substrates, such as PVC cards or cloth sheets, using a printing sheet, the image-receiving layer-bearing sheet as described above and the method for transferring the image-receiving layer as set out hereinbefore. These procedures are within the scope of the invention. Figs. 6A to 6D show a procedure for forming a thermal transfer image according to one embodiment of the invention. In this embodiment, the thermal transfer image-receiving layer 2 formed on the substrate 4 according to the procedures illustrated in Figs. 3A to 3C and 4A to 4C, respectively, is first provided and superposed thereon with a printing sheet 9. The printing sheet 9 has a synthetic paper support 9b and an image-receiving layer 9a on which a thermal transfer image 8 made of a cationic dye has been previously formed. The superposition is such that the image 8 is facing with the receiving layer 2 as shown in Fig. 6B. If necessary, an adhesive layer 3 as shown in Fig. 2 or an adhesive sheet 5 as shown in Figs. 3A to 3C may be provided between the substrate 4 and the layer 2 as in the foregoing embodiment. Subsequently, the superposed sheets are hot pressed, for example, by passage between hot rolls 10, so that the cationic dye thermal transfer image 8 is re-transferred from the image-receiving layer 9a of the printing sheet 9 to the thermal transfer image-receiving layer 2 thereby forming a thermal transfer image 2a as shown in Fig. 6C. The cationic dye of the thermal transfer image 2a is held and fixed with the layer compound through ion exchange reaction. Finally, the printing sheet 9 is separated from the thermal transfer image-receiving layer 2 as shown in Fig. 6D. Figs. 7A to 7D schematically show a procedure of forming a thermal transfer image on an intended type of substrate according to another embodiment of the invention. This embodiment comprises forming a thermal transfer image on an ordinary printing sheet, and re-transferring the image to a thermal transfer image-receiving layer of the sheet of the type shown in Fig. 1 prior to attachment of the receiving layer to an intended type of substrate. More particularly, the image-receiving layer 2 of the sheet shown in Fig. 1 is first provided. A printing sheet 9, which has an image-receiving layer 9a formed on a synthetic paper 9b and formed with a thermal transfer image 8 made of a cationic dye, is then superposed on the sheet of Fig. 1 so that the image-receiving layer 9a and the layer 2 are facing each other as shown in Fig. 7B. The superposed sheets are hot pressed such as by passage through heat rolls 10, thereby permitting the cationic dye of the thermal transfer image 8 from the image-receiving layer 9a of the printing sheet 9 to be re-transferred to the layer 2 to form a thermal transfer image 2a as shown in Fig. 7C. The thus re-transferred cationic dye is held and fixed with the layer compound in the layer 2 through ion exchange reaction therebetween. Next, the sheet having the image-receiving layer 2 on which the thermal transfer image has been formed is used to transfer the image-bearing layer 2 to a substrate 4, on which the thermal transfer image 2a is to be formed, according to any of the procedures set out hereinbefore with respect to Figs. 3A to 3C, 4A to 4C and 5A to 5C. This is particularly shown in Fig. 7D. Like the foregoing embodiments, an adhesive layer or sheet may be provided between the substrate 4 and the layer, if necessary. Aside from the foregoing embodiments of the invention, the sheet of the invention capable of releasing the thermal transfer image-receiving layer therefrom may be used as a protective sheet for a printing sheet on which a thermal transfer image has been previously formed. In this case, the image-receiving layer 2 is transferred to and attached on an image-receiving layer of a printing sheet on which a thermal transfer image made of a cationic dye has been previously formed. The layer compound used in the present invention has a layer structure which has generally recurring units of a three-layer structure having a fundamental octahedron skeleton. In a non-treated and natural state, layer water and alkali metal ions which are ion exchangeable cations are held inbetween the respective layers. This is particularly shown in Fig. 8. A non-treated layer compound 11 has ion exchangeable sodium ions 12 between the layers thereof. The layer distance is taken as d1 as shown. In the practice of the invention, it is preferred to use, as the layer compound, those compounds which have better ion exchangeability than non-treated compounds. More particularly, the layer compound 11 is swollen with water, to which organic cations such as quaternary ammonium ions 13 are added. By the addition, ion exchange takes place wherein the quaternary ammonium ions 13 are taken inbetween the layers instead of the sodium ions 12 as shown in Fig. 9. Owing to the presence of the quaternary ammonium ions 13 inbetween the layers, a layer distance d2 becomes larger than the layer distance d1 of the non-treated layer compound. This permits better ion exchangeability with hydrophobic cationic dyes. The layer compound imparted with better ion exchangeability has the quaternary ammonium ions 13 having a hydrophobic chain held therein, so that when mixed with and dispersed in non-aqueous binder polymers, the compound swells. When a thermal transfer image made of a hydrophobic cationic dye is formed on or in the thermal transfer image-receiving layer containing a swollen layer compound thereon, the hydrophobic cationic dye is miscible with the non-aqueous dye image-receiving layer and is taken in the respective layers of the layer compound. In the layers, ion exchange takes place between the quaternary ammonium ions 13 and a cationic dye 14. The cationic dye 14 which has been taken inbetween the layers of the layer compound 11 is ionically bonded to the layer compound 11 and securely fixed in the image-receiving layer. Accordingly, if the image-receiving layer in which the thermal transfer image made of the hydrophobic cationic dye has been formed is brought into contact with a material having a large quantity of plasticizer over a long time, the dye ionically bonded to the layer compound is prevented from transferring to the contacted material. Further, the solvent resistance of the cationic dye image can be drastically enhanced. The invention is more particularly described by way of examples. Example 1 20 g of synthetic saponite (available from Kunimine Ind. Co., Ltd. under the designation of Smecton SA) was provided as a layer compound and dispersed and swollen in one liter of water. Ethanol was added to the resultant dispersion in the same amount as that of the dispersion, followed by dropping 13.2 g (20 mg equivalents) of tetra-n-decylammonium bromide dissolved in 200 cc of ethanol under agitation. The mixture was allowed to stand over one week, whereupon granular coagulates or precipitates were settled down. The precipitates were separated from the dispersion by filtration and washed with a large amount of ethanol to remove unreacted quaternary ammonium salt therefrom. Subsequently, the thus washed precipitate was dried at room temperature under reduced pressure to obtain a purely white, hydrophobic powder of the layer compound. The thus obtained layer compound and other ingredients were formulated as indicated in Table 1 and uniformly mixed by means of a jar mill to obtain a composition for forming a thermal transfer image-receiving layer. The composition was applied onto one side of a 50 µm thick polyethylene terephthalate release base sheet (available from Toray Co., Ltd. under the designation of S-10) in a dry thickness of about 10 µm by use of a wire bar, followed by drying with hot air of 120°C for 2 minutes. Thus, a sheet capable of releasing a thermal transfer image-receiving layer therefrom was obtained. The thermal transfer image-receiving layer of the sheet was superposed on a currently employed PVC card (made by Dai Nippon Printing Co., Ltd.), followed by hot pressing by use of a hot press (MS-Pouch-H-140 available from Meiko Co., Ltd.) and separating the release base sheet therefrom to obtain a PVC card having the thermal transfer image-receiving layer thereon. Separately, ink layer compositions comprising hydrophobic cationic dyes and having formulations indicated in Tables 2 to 4, respectively, were each applied in a dry thickness of about 1 µm onto a primer layer of a polyethylene terephthalate film (PET film) having a heat-resistant lubricating layer on a side opposite to the primer layer and dried with hot air of 120°C for 2 minutes. As a result, yellow, cyan and magenta ink ribbons were, respectively, obtained. These ink ribbons were employed to form a thermal transfer image on a currently employed printing sheet having a cellulose image-receiving layer (VPM-30 STA available from Sony Corporation). The thermal transfer image-receiving layer of the PVC card and the image-received layer of the printing sheet were superposed, followed passage through a hot pressing device (MS-Pouch H-140 available from Meiko Co., Ltd.) so that the cationic dyes in the image-received layer of the printing sheet were re-transferred to the image-receiving layer of the PVC card, thereby forming a thermal re-transfer image on the PVC card. The fixing properties of the thermal re-transfer image of the PVC card were tested and evaluated according to the following procedures. Fixing Tests 1 to 3: 1. The thermal transfer image-receiving layer of the PVC card was allowed to stand for 14 days while keeping it in contact with an artificial leather made of polyvinyl chloride. Thereafter, it was visually observed and evaluated whether or not the dyes were re-transferred or migrated to the artificial leather and the thermal transfer image was damaged. The results are shown in Table 5. In the table, the mark "o" means the case where no dye was migrated to the artificial leather with the thermal transfer image suffering no change in appearance. The mark "x" means the case where dyes are migrated to the artificial leather and the thermal transfer image underwent some changes. 2. The image-received layer of the PVC card was attached with toluene. Thereafter, it is visually evaluated whether or not the dyes are dissolved out in the toluene with the result that the image was impeded. The results are also shown in Table 5. In the table, the mark "o" indicates the case where no dye was dissolved out in toluene and the mark "x" indicates the case where the dyes were dissolved out in toluene with the image undergoing some changes. 3. The image-received layer of the PVC card was attached with a cyanoacrylate instantaneous adhesive. Then, it was visually evaluated whether or not the dyes were dissolved out In the adhesive and the thermal transfer image was eventually impeded. The results are shown in Table 5. IN the table, the mark "o" indicates the case where the dyes were not dissolved out in the adhesive with the image suffering no change. The mark "x" indicates the case where the dyes were dissolved out in the adhesive with the image suffering some change. The results are shown in Table 5. As will be apparent from Table 5, the fixing properties of the thermal transfer image formed on the PVC card were good. Comparative Example 1 A thermal transfer image was formed in the same manner as in Example 1 on a currently employed PVC card (made by Dai Nippon Printing Co., Ltd.). The fixing properties of the thermal transfer image of the PVC card were tested and evaluated in the same manner as in Example 1. The results are shown in Table 5. As will be apparent from Table 5, the fixing properties were not good. Example 2 The sheet capable of releasing an image-receiving layer fabricated in Example 1 was superposed at the side of the image-receiving layer with an adhesive sheet (HItachi Video Print Kit available from Hitachi Ltd.), followed by hot pressing (MS-Pouch H-140 available from Meiko Co., Ltd.) to form the adhesive sheet layer on the thermal transfer image-receiving layer. Separately, a thermal transfer image was formed on a printing sheet in the same manner as in Example 1. Next, the release base sheet was removed from the sheet capable of releasing the receiving layer. Then, the adhesive sheet layer was provided on a 100% cotton cloth whereas the thermal transfer image of the printing sheet was placed on the thermal transfer image-receiving layer exposed by the removal of the sheet, followed by heating with a warm iron. By this, the thermal transfer image-receiving layer was bonded to the cloth and the thermal transfer image of the printing sheet was re-transferred to the exposed image-receiving layer. Thus, the cloth had the thermal transfer image thereon. The fixing properties of the image on the cloth were tested and evaluated in the following procedures. Fixing Tests 4 and 5 4. The cloth was immersed for 30 seconds in perchloroethylene, which was ordinarily used as a solvent for dry cleaning. Then, it was visually observed and evaluated whether or not the dyes were dissolved out in perchloroethylene with the thermal transfer image being damaged. The results are shown in Table 6. In the table, the mark "o" indicates the case where the dyes were not dissolved out in perchloroethylene without any change of the thermal transfer image. The mark "x" indicates the case where the dyes were dissolved out in perchloroethylene and the image underwent some changes. 5. Iron balls and the cloth were placed in perchloroethylene and mixed in a jar mill for 3 hours. Thereafter, it was visually observed and evaluated whether or not the dyes were dissolved out in perchloroethylene and the thermal transfer image was damaged. The results are shown in Table 6. In the table, the mark "o" indicates the case where the dyes were not dissolved out in perchloroethylene without any change of the thermal transfer image. The mark "x" indicates the case where the dyes were dissolved out in perchloroethylene and the image underwent some changes. As will be apparent from Table 5, the fixing properties of the thermal transfer image formed on the cloth were good. Comparative Example 2 A thermal transfer image was formed on a printing sheet in the same manner as in Example 1. The thermal transfer image was re-transferred from the printing sheet to a cloth by use of a commercially available printing kit (HItachi Video Print Kit of Hitachi Ltd.). The fixing properties of the thermal transfer image of the cloth were similarly tested and evaluated. The results are shown in Table 6. The results of Table 6 reveal that the thermal transfer image formed on the cloth was not satisfactory with respect to the fixing properties. As will be apparent from the foregoing, the methods of the invention which are adapted for the formation of images according to the thermal transfer systems ensure improved fixing properties of cationic dyes in image-receiving layers. Moreover, the image-receiving layer, on which an intended thermal transfer image has been formed or not formed yet, can be readily transferred and bonded to various types of substrates such as PVC cards, cloths and the like.

Claims: A method for forming a thermal transfer image on a substrate, the method comprising the steps of providing a printing sheet (9) comprising an image-receiving layer (9a) on which a thermal transfer image (8) made of a cationic dye has been formed, providing a sheet of the type including a release base sheet (1) and a thermal transfer image receiving layer (2), said thermal transfer image-receiving layer (2) being made of a dispersion, in a resin binder, of a layer compound capable of fixing cationic dyes through ion exchange reaction therewith, superposing the image-receiving layer (9a) of the printing sheet (9) on said thermal transfer image-receiving layer (2) of said sheet, hot pressing the superposed layers (2, 9a) to re-transfer the cationic dye image on said thermal transfer image-receiving layer (2) thereby causing the cationic dye image to fix through ion exchange reaction with the layer compound in said thermal transfer image-receiving layer (2). A method according to claim 1, characterized by the steps of superposing said thermal transfer image-receiving layer (2) on which a thermal transfer image (8) is to be formed in face-to-face relation with the substrate (4) and peeling of said release base sheet (1) from said thermal transfer image-receiving layer (2) prior to the step of superposing the image-receiving layer (9a) of the printing sheet (9) on said thermal transfer image-receiving layer (2). A method according to claim 1, characterized by the step of transferring the thermal transfer image-receiving layer (2) on which the thermal transfer image (8) has been formed to the substrate (4) after the step of hot pressing the superposed layers (2, 9a).

Inventors: FUJIWARA YOSHIO, HIDA MASANOBU, ISAJI KAORI, ISOGAI MITSUHIRO C O SONY CORP, ITO KENGO, FUJIWARA, YOSHIO, HIDA, MASANOBU, ISAJI, KAORI, ISOGAI, MITSUHIRO, ITO, KENGO, FUJIWARA, YOSHIO, C/O SONY CORPORATION, HIDA, MASANOBU, C/O SONY CORPORATION, ISAJI, KAORI, C/O SONY CORPORATION, ISOGAI, MITSUHIRO, C/O SONY CORPORATION, ITO, KENGO, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: B41M5
IPC codes: B41M5